Acoustic wave device facilitates frequency filtration to enable the transmission and receiving of signals at a specific frequency bandwidth. Such device is conventionally employed in broadcast radio, television and mobile communication applications. The multitude functionality of these passive acoustic wave devices are achieved by integrating them with active circuits to form various devices like oscillators, active filters, low noise amplifiers, mass sensors, temperature sensors, etc. These electronic circuits that are fabricated by complementary-metal-oxide semiconductor, CMOS technology, and the acoustic devices that are fabricated by micro-electro mechanical systems (MEMS) technology, may be mounted on a laminated board or silicon interposer.
Generally, integration of the electronic circuits and the acoustic devices are accomplished through monolithic or heterogeneous integration methodologies where the acoustic device is built on top of the electronic circuits. As compared to heterogeneous integration, monolithic integration offers a more elegant solution. An example of a monolithic integrated device described in U.S. Patent Application Publication No. US2006/0202779 comprises a substrate, an electronic circuitry supported by the substrate, an acoustic isolator over the electronic circuitry and an acoustic resonator on the acoustic isolator that transduces bulk acoustic waves. The acoustic resonator is vertically integrated with the electronic circuitry in a single monolithic device. Such a feature of this device shortens the signal traveling distance between the acoustic resonator and the electronic circuitry as well as reduces the number of connections, thus resulting in the improvements in performance and sensitivity of the monolithic integrated device, and reducing the size of the monolithic integrated device while increasing the number of acoustic resonator components and electronic circuitry components that can be fabricated within a given area of the substrate compared to monolithic integrated devices in which the acoustic resonators are laterally integrated with electronic circuitry.
Another example of a monolithic integrated device disclosed in U.S. Pat. No. 5,260,596 describes a monolithic circuit chip that is integrated with a bulk structure resonator. The chip contains multiple integrated circuit components fabricated as part of a semiconductor substrate that is mounted with a spring for supporting a mass. An exciting means is included in this invention for applying a varying electrostatic force to the mass for inducing a mechanical vibration in the mass. A cavity fabricated on the semiconducting substrate providing room for the mechanical vibration to occur. Other embodiments of this invention incorporate the use of non-piezoelectric mechanical resonators, quartz crystal resonators and thin film piezoelectric resonators that can generate either surface acoustic waves or bulk acoustic waves.
Conventional monolithic integrated devices, in particular those that are configured to have the acoustic device being built on top of the electronic circuitry of the CMOS device, pose complexity and compatibility issues between the acoustic device and the CMOS device, which causes a trade off in the functionality of the acoustic device. Hence, the present invention disclosed herein aims to provide solutions to these problems.